Anti-submarine fight

The anti-submarine fight ( ASM , in English: anti-submarine warfare - ASW ) indicates the whole of the tactics of combat and protection against the threat represented by the Sous-marin S.

The anti-submarine fight is a “hunting” practiced with several complementary means, surface vessels equipped with Sonar S, planes of maritime patrol, helicopters ASM and submarines of attack, whose central part is generally a anti-submarine frigate on which is taken on board the “owner” of the operation.

Types of operations

Preventive operations

The preventive operations consist in supervising a priori a zone in which is likely to operate or to forward submarines. Units ASM carry out a research in this zone or establish stoppings in the zones of passages obliged. For example, during the Cold war, the outlets of the sea of Norway on the Atlantic (straits between Greenland, Iceland and British Isles, GIUK for the english-speaking) was zones of patrol for the units of NATO, to try to intercept the submarines of the Soviet Marine.

These operations are long, tiresome and often disappointing, but they reduce the capacities of action of the submarines.

The principal tool of these operations is the maritime plane of patrol. The fixed systems of acoustic monitoring of the oceans (SOSUS) also take part in this kind of action.

Defensive operations

The defensive operations consist in protecting from the invaluable units (a air and sea Groupe or a amphibious group) or a convoy of trading vessels against the underwater threat.

This type of operations was particularly illustrated in the history by the escort of the convoys during the two world wars. (see the articles on the Battle of the Atlantic)

The ships of escort, supplemented if possible by helicopters and planes and possibly by nuclear underwater of attack (SNA) are laid out out of mobile screens around the units to protect, preferably placed in such way that the attacking submarine has to cross a succession of obstacles (in-depth defense) before being in position of shooting.

These safety devices require many units ASM. Relatively effective against traditional submarines, because then respective kinematics impose only one screen on the front one, these devices are it much less against SNA, rapids, which also require a protection on the back. In addition, the technological advances carried out on the torpedes of the submarines, whose ranges increased much, and especially the advent of the anti-ship missile with change of medium make that the tactical balance does not lean today a side of the escort.

Offensive operations

The offensive operations are carried out by groups of frigates ASM, with their helicopters (groups “ Hunters-Killers ”), possibly supplemented by a maritime plane of patrol, which act on alarm, either within an escort, or independently following a detection at the time of a preventive operation.

Tactics

The tactics of the commander of operation ASM consist in, generally, leading the submarine in a trap, by using active sonars to force it to flee towards passive sonars.

It thus will use the sonars active of the frigates (of hull or towed), that of its helicopters (soaked sonars) and the active acoustic buoys released by the maritime plane of patrol to detect the adversary or to make it flee towards the passive sonars of a submarine of attack or the passive acoustic buoys of the maritime plane of patrol, which them are undetectable by the submarine.

In the event of contact with the active sonars of the frigates, those remain remote and make take off or to rejoin their helicopters for checking and possibly attacks with the torpedo. In the same way, the maritime plane of patrol, after detection on its passive buoys, checks the contact with its Détecteur of magnetic anomaly, attacks itself or makes rejoin by guiding them, of helicopters ASM or the frigates which contribute it with tracking and the attack.

The anti-submarine tactics are multiple: they require a very thorough drive, a skill and perseverance and team spirit much. The conditions of the environment are very variable: small funds or deep seas, conditions of propagation of the sound in water, meteorology, noises biological or of the commercial traffic. It is the field of random and the probabilities.

Actors and equipment

Frigate ASM

Frigate ASM is a combat building of a Tonnage of about 4 to 5.000 tons, whose principal system of weapons is dedicated to fight ASM:

active sonars low frequency of stem and towed (VDS: variable depth sonar );
passive sonar towed (ALR: vertical wire aerial towed)
torpedes and sometimes missiles torpedo spar (standard Malafon French or American Asroc);
helicopters embarked ASM.

These buildings have also means of fight of surface (sea-to-sea missiles) and a strong capacity of anti-aircraft self-defense (missiles sea air with short and average range).

Helicopter ASM

Helicopter ASM is an average helicopter armed with torpedes and provided with a sonar. This sonar is suspended with a winch and the helicopter, in hovering, comes “to soak it” (from where the name of “sonar soaked”) with the immersion most favorable to detection. In contact with a submarine, it proceeds by jumps (stations) to track it.

Helicopters ASM embarked on frigate represent a great threat for the submarine. Acting as group of two or three, invulnerable with respect to the submarine, they has a great capacity of behavior of contact and tracking. They are also used by the frigate to check a contact obtained at long distance and for the attack, the frigate remaining then out of reach weapons of the submarine.

The maritime plane of patrol

The maritime plane of patrol in fight ASM is able to remain several hours on its zone of patrol, which it will systematically explore with several sensors before attacking the Sous-marin with torpedes.

The submarine

The best submarine chaser is certainly the submarine of attack itself: it has “hearing” much finer than the frigates and the aircraft. In patrol at fallback speed, towing with three kilometers behind the antenna of a passive sonar to very low frequency, it is with the mounting of the least indiscretion of the unfavourable submarine (too high speed, abrupt change of immersion, noises of installations on board). For little that it is quieter than its adversary, it has on him a decisive advantage. On the other hand, if the two submarines are as quiet one as the other, the fight is connected with a combat in the most total darkness.

However, the co-operation with other units ASM is difficult and constraining for the submarine: it obliges it to come to the periscopic immersion to communicate, therefore to make an indiscretion, and if required to leave the immersion of better listening. This is why, generally, SNA will be in indirect support of the force to be protected.

See too

Sonar
Underwater SOSUS
naval War § 2.2 the underwater war
the Decoy-ships, ship of alleviating appearance, but armed, built for the anti-submarine fight.

External bonds

the anti-submarine fight Site of the National marine

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